Modified fibers for use in the formation of thermoplastic fiber-reinforced composite articles and process

ABSTRACT

A surface-modified fibrous material is provided for incorporation in a thermoplastic matrix to form a fiber-reinforced composite article. Good binding between the fibrous material and the thermoplastic matrix is achieved through the presence of finely roughened surfaces on the fibers of nanoparticles of an inorganic material. Such nanoparticles are provided from an alkaline aqueous size composition containing the nanoparticles dispersed therein (as described). The fibrous material may be provided in continuous or discontinuous form. In a preferred embodiment glass fibers are initially provided in continuous form followed by cutting into discontinuous lengths and drying with the retention of the nanoparticles on the surfaces of the fibers. The surface-roughened fibrous material is incorporated in a thermoplastic matrix as fibrous reinforcement with the application of heat whereby the thermoplastic matrix is rendered melt processable. In preferred embodiments injection or compression molding is utilized. Improved long-fiber thermoplastics also may be formed to advantage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.11/645,963 filed Dec. 27, 2006.

FIELD OF THE INVENTION

The subject invention pertains to the formation of improved fibers forincorporation in a thermoplastic matrix to form a fiber-reinforcedcomposite article. Enhanced binding between the thermoplastic matrix andthe glass fiber reinforcement is made possible.

DESCRIPTION OF RELATED ART

Various binders and sizing compositions are known to improve thehandling characteristics of fibrous materials.

When fibers are incorporated in the continuous phase of a thermoplasticpolymeric matrix material to serve a reinforcing role it is advantageousthat the fibers also bind to some degree to the continuous phase of thematrix material of the resulting fiber-reinforced composite article.Otherwise, various forms of product failure may occur during use. Forinstance, various coupling agents commonly are being employed to helpthe fiber reinforcement better attach to the matrix material of thecontinuous phase. It is also desirable that minimal color is displayedin the final fiber-reinforced composite article.

It has been proposed to prepare an epoxy thermoset resin, whichincorporates a woven continuous filament fabric, in which a sizingpackage including colloidal silica is applied to the woven fabric priorto the incorporation followed by vacuum assisted resin transfer molding.See, for instance, Army Research Laboratory Report No. ARL-TR-3241 (July2004), and R. E. Jensen, S. H. McKnight, Composites Sci. Tech., Vol. 66,Pages 509 to 521 (2006).

It is an object of the present invention to provide an improved processas well as the resulting product for forming modified fibers suitablefor incorporation in a thermoplastic matrix to form a fiber-reinforcedcomposite article.

It is another object of the present invention to provide an improvedprocess as well as the resulting product for forming a fiber-reinforcedthermoplastic composite article.

It is another object of the present invention to providefiber-reinforced composite articles which may display improved toughnesscombined with good color.

It is a further object of the invention to provide fiber-reinforcedmolded composite articles which may display good color, an improvedmechanical property, and a reduced size requirement when compared to aconventional size.

These and other objects of the invention, as well as the scope, natureand utilization of the invention will be apparent to those skilled inthe art from the following detailed description.

SUMMARY OF THE INVENTION

A process, as well as the resulting product, is provided for formingmodified fibers having roughened surfaces suitable for incorporation ina thermoplastic matrix to form a fiber-reinforced composite articlecomprising:

(a) applying as a coating to the surface of a fibrous material analkaline aqueous size composition comprising a dispersion ofnanoparticles of an inorganic material, and

(b) drying said coating present on said fibrous material to provide aroughened surface on said fibrous material as the result of the presenceof said nanoparticles of said inorganic material.

A process, as well as the resulting product, is provided for formingmodified discontinuous glass fibers suitable for incorporation in athermoplastic matrix and the formation of a fiber-reinforced compositearticle by injection or compression molding which displays an enhancedmechanical property comprising:

(a) adhering nanoparticles of an inorganic material that are dispersedin an alkaline aqueous size composition to the surfaces of glass fiberswhich are present in continuous form to provide finely roughenedsurfaces on the continuous glass fibers as the result of the presence ofthe nanoparticles of the inorganic material, and

(b) cutting the continuous glass fibers into discontinuous lengths whileretaining the roughened surfaces on the glass fibers as the result ofthe presence of the nanoparticles of the inorganic material.

A process, as well as the resulting product, is provided for forming afiber-reinforced thermoplastic composite article comprising:

(a) applying as a coating to the surface of a fibrous material analkaline aqueous size composition comprising a dispersion ofnanoparticles of an inorganic material,

(b) drying said coating present on said fibrous material to provide aroughened surface on said fibrous material as the result of the presenceof said nanoparticles of said inorganic material, and

(c) incorporating said fibrous material bearing said roughened surfacein a thermoplastic matrix as fibrous reinforcement with the applicationof heat whereby said thermoplastic matrix is rendered melt processable.

A process, as well as the resulting product, is provided for forming adiscontinuous glass fiber-reinforced thermoplastic composite articlecomprising:

(a) adhering nanoparticles of an inorganic material that are dispersedin an alkaline aqueous size composition to the surfaces of glass fiberswhich are present in continuous form to provide finely roughenedsurfaces on the glass fibers as the result of the presence of thenanoparticles of the inorganic material,

(b) cutting the continuous glass fibers into discontinuous lengths whileretaining the roughened surfaces on the glass fibers as the result ofthe presence of the nanoparticles of the inorganic material,

(c) extruding the discontinuous glass fibers having said finelyroughened surfaces together with a thermoplastic matrix wherein thesurface-attached nanoparticles of inorganic material serve to promotethe secure bonding of the discontinuous glass fibers within thethermoplastic to form a material suitable for molding, and

(d) injection or compression molding said material incorporating thediscontinuous glass fibers having the finely roughened surfaces to forma fiber-reinforced thermoplastic composite article which displays anenhanced mechanical property.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention makes possible the efficient formation of qualitythermoplastic fiber-reinforced composite articles wherein enhancedbinding between fibrous reinforcement and the thermoplastic matrix ismade possible. In accordance with the concept of the present invention,nanoparticles of an inorganic material initially are well dispersedwithin an alkaline aqueous size composition. The nanoparticles of aninorganic material are relatively inert under the conditions that areencountered in the size composition and commonly possess an averageparticle size of approximately 3 to 40 nm, preferably approximately 3 to10 nm. Such particle size can be determined by the use of particle sizeanalyzers that are being manufactured by companies such as Malvern ofWorcestershire, United Kingdom, Beckman Coulter of Fullerton, Calif.,U.S.A., and others. Inorganic nanoparticles displaying a specificsurface area 300 m²/g commonly possess an average particle size ofapproximately 10 nm, and inorganic nanoparticles displaying a specificsurface area of 650 m²/g commonly possess an average particle size ofapproximately 3 nm. In preferred embodiments, the nanoparticles of aninorganic material are provided as substantially amorphous spheres;however, other particle shapes are suitable for use and may havedifferent ratios of surface areas to their sizes.

In preferred embodiments, the nanoparticles of an inorganic material aresilica of the specified particle size. Representative colloidal silicananoparticles for use in the present invention are commerciallyavailable from Eka Chemicals, Inc. of Marietta, Ga., U.S.A. underdesignations of Bindzil® or from Grace Davison of Columbia, Md., U.S.A.under the Ludox® designations. Other representative nanoparticles of aninorganic material suitable for use in the present invention include,but are not limited to, clays, including montmorillonite-type clays,glass, nanosized particles of metals or non-metals such as titaniumdioxide, zinc oxide, barium oxide, silver, cerium gadolinium oxide,palladium, iron ferrite nanoparticles, aluminium polyphosphate,nanodiamonds, or other functionalized or unfunctionalized inorganicnanoparticles having modified or unmodified surfaces. A representativeamino-functionalized clay is commercially available from theKentucky-Tennessee Clay Company of Mayfield, Ky., U.S.A. under the Amlok321 designation. Mixtures of the nanoparticles may be utilized.

The fibrous material suitable for incorporation in a thermoplasticmatrix which is surface-roughened in accordance with the concept of thepresent invention may be provided in continuous or discontinuous form.For instance, the fibers can be mineral fibers or polymeric fibers whichpossess sufficient thermal stability to withstand the heatedmelt-processable thermoplastic matrix material when forming afiber-reinforced composite article as described hereafter. Highperformance polymeric fibers may be utilized which possess a greaterthermal stability than the thermoplastic matrix material utilized whenforming a fiber-reinforced composite article. Also, carbon fibers ornatural fibers may serve as the fibrous reinforcement. The fibrousmaterial preferably comprises glass fibers. Representative glass fibersare E-glass, C-glass, A-glass, AR-glass, D-glass, R-glass, S-glass, etc.Such glass fibers can be initially supplied as long multifilamentaryrovings or tows of infinite length. Single fibers thereof commonlypossess average fiber diameters of approximately 2 to 50 μm, andpreferably approximately 7 to 30 μm. It will be understood, however,that fiber diameters can be adjusted to meet the reinforcementrequirements of specific end uses.

The nanoparticles of an inorganic material commonly are provided in thealkaline aqueous size composition when applied to continuous glassfibers in a concentration of 1 to 90 percent based on the totalformulation solids, preferably in a concentration of 2 to 40 percentbased on total formulation solids, and most preferably in aconcentration of 5 to 40 percent based on total formulation solids. Allpercentages are based on the solids weight.

The alkaline pH of the size composition is obtained by the use of othersize components, and may be adjusted so as to provide for thesubstantial dispersion of the nanoparticles of an inorganic materialtherein. The optimum alkaline pH is influenced by the alkalinecontribution of the components present in the aqueous dispersion andcommonly is within the range of 7.5 to 13, and preferably within therange of 8 to 11.

The remaining components of the alkaline aqueous size composition may bein accordance with previously known size compositions provided thenanoparticles of an inorganic material are compatible therewith and theresulting composition following inclusion of the inorganic nanoparticlesis otherwise capable of functioning as a size for fibrous glassmaterials. Commonly, the aqueous size composition will also include atleast one silane, at least one surfactant or lubricant, and at least onepolymeric film-former.

The silanes may be of the reactive type, the non-reactive type, or acombination of reactive and non-reactive silanes. Non-reactivehydrophobic silanes are known to inhibit water adsorption at theinterface between the glass fibers and a matrix. When a combination ofreactive and non-reactive silanes is utilized, the relative quantitiesof reactive to non-reactive types commonly is in the range of 20:80 to99:1, and most preferably in the range of 55:45 to 70:30. The silanes ofthe reactive type serve as coupling agents between the glass fibers andthe thermoplastic matrix. The reactive silanes commonly contain asilicone head(s) and a tail(s) containing a functional group or groupsthat can react with the thermoplastic matrix. These include primary,secondary, or tertiary amines, vinyl, styryl, alkynyl, methacryloyl,acryloxy, epoxy, thio, sulphide, ureido, isocyanate, oxime, ester,aldehyde, and hydroxy moieties in either unprotected or protected form.The silicone head can be substituted with groups such as ethoxy,methoxy, methyldimethoxy, methydiethoxy, isopropoxy, acetoxy, etc.Representative reactive silanes include 3-aminopropyltriethoxysilane,3-aminopropyldiethoxymethylsilane, 3-aminopropyltrimethoxysilane,N-(2-aminoethyl)-3-aminopropyltrimethoxysilane,N-(2-aminoethyl)-3-aminopropyl-methyldimethoxysilane,(3-glycidoxypropyl) trimethoxysilane,2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,3-isocyanotopropyltriethoxysilane, vinyltrimethoxysilane,3-ureidopropyltrimethoxysilane, (3-aminopropyl)methyldiethoxysilane,3-glycidopropyltriethoxysilane, vinyltriacetoxysilane,mercaptopropyltriethoxysilane, 4-amino-3,3-dimethylbutyltriethoxysilane,N-butyl-3-aminopropyltrimethoxysilane, etc. The non-reactive silanes arecapable of occupying reactive sites on the glass fibers but do nototherwise chemically react with the thermoplastic polymeric matrix. Thenon-reactive silanes commonly include silanes that contain aliphatic,aromatic, aliphatic or aromatic fluorinated, halogen, and otherfunctionalities. Representative non-reactive silanes includemethyltrimethoxysilane, propyltriethoxysilane, propyltrimethoxysilane,3,3,3-trifluoropropyltrimethoxysilane, iso-butyltriethoxysilane,octyltriethoxysilane, hexadecyltriethoxysilane,1,2-bis(trimethoxysilyl)decane, etc. The silane(s) commonly are providedin the alkaline aqueous size composition in a concentration of 0.5% to75% based on the total solids of the sizing, and preferably in aconcentration of 5% to 50% based on the total solids of the sizecomposition. A mixture of two or more silanes can be used.

A surfactant or lubricant commonly is included in the alkaline aqueoussize composition to aid in the processing of the fibers during and afterapplication of the size composition. Preferred surfactants or lubricantsare the mono- or diesters of a fatty acid or oil reacted withpolyethylene glycol, having hydrophilic and lipophilic areas. Apreferred surfactant or lubricant of this type is Mapeg® 200 ML PEG(200) ester monolaurate that is commercially available from the BASFCorporation, Mount Olive, N.J., U.S.A. Another preferred surfactant orlubricant is Polyox WSR301 available from the Dow Chemical Company,Midland, Mich., U.S.A. Other representative surfactants or lubricantsinclude those available under the Cat-X and Emery 6717 designations. Thesurfactants or lubricants commonly are provided in the size compositionin a concentration of approximately 0.001 to 25 percent based on thetotal formulation solids, and preferably in a concentration ofapproximately 0.001 to 10 percent based on the total formulation solids.In some cases, other sizing components may function as lubricants and/orsurfactants and addition of a separate lubricant may be unnecessary.

Additionally, a polymeric film-former that is compatible with thethermoplastic matrix commonly is included in the alkaline aqueous sizecomposition to further aid in the adherence of the nanoparticles to theglass fibers and the glass fibers to the thermoplastic matrix. Suchfilm-formers may be of the non-ionic, cationic, or anionic types.Representative film-formers for polypropylene matrix are provided asmodified polypropylene emulsions. Other polymeric matrices are typicallyserved by emulsions of modified or unmodified urethanes, modified orunmodified polyethylenes, modified or unmodified epoxy resins, anddispersions or emulsions of other chemicals, as well as various mixturesthereof. A preferred polymeric film-former is a nonionic emulsion ofpolypropylene grafted with maleic anhydride that is commerciallyavailable from Michelman, Inc. of Cincinnati, Ohio, U.S.A., under theMichem® ME 91735 designation. Other preferred film-formers includeNeoxil 777 from DSM of Heerlen, The Netherlands, and PP2-01 or XM10075from Hydrosize Technologies of Raleigh, N.C., U.S.A. The film formerscommonly are provided in the alkaline aqueous size in a concentration ofapproximately 10 to 95 percent by weight based on the total formulationsolids, and preferably in a concentration of 20 to 85 percent by weightbased on the total formulation solids.

The alkaline aqueous size composition optionally may include furtherpolymeric emulsion components, adhesion promoters, solvents,emulsifiers, pigments, anti-migration aids, UV absorbers, biocides,colorants, dyes, anti-static agents, antioxidants, HALS, processingaids, defoamers, antifoamers, combinations of the above and othercomponents required or preferred for specific applications.

The alkaline aqueous size composition may be applied by any techniquecapable of coating the fibrous material with the flowable sizecomposition containing the dispersion of inorganic nanoparticles thatproperly wets the fiber surfaces. In a preferred embodiment, a kiss-rollapplicator may be utilized to apply the composition to a continuousmultifilamentary material. Other equipment arrangements suitable forapplying the size composition include dipping, spraying, or any otherprotocol suitable for delivery of the size composition to the glassfibers. Commonly, the alkaline aqueous size composition possesses aviscosity of approximately 1 to 5000 mPa s, and preferably approximately10 to 1000 mPa s at the time of its application to the continuous glassfibers.

Commonly, the adhering nanoparticles are provided on the surface of thefibrous material in a concentration of approximately 1 to 75 percent byweight based on the weight of the total sizing solids following theremoval of the aqueous component, and preferably in a concentration ofapproximately 10 to 40 percent by weight. One has the option ofutilizing a lesser overall quantity of the alkaline aqueous sizecomposition when compared to size compositions of the prior art. Theuniform and intimate coating of the surfaces of the fibrous material canbe promoted by the adjustment of filament contact angles, adjustment ofcoating roll speeds, applicator roll dimensions and/or theircomposition, fiber pull speeds, pressure and throughput of the potsprays, air flow, contents of the size composition, etc. Such coatingparameters may vary widely depending on the forming and processing needsand preferences and are known by those skilled in the art.

In a preferred embodiment, the fibrous material (e.g., continuous glassfibers) bearing the adhering nanoparticles of an inorganic material areoptionally cut into discontinuous lengths while retaining the roughenedsurfaces of the fibrous material as the result of the continued presenceof the attached nanoparticles of an inorganic material. Suchdiscontinuous lengths commonly measure approximately 2 to 100 mm, andpreferably approximately 3 to 50 mm, and are well suited for serving asimproved fibrous reinforcement in a thermoplastic matrix material. Anyconventional fiber chopping equipment can be utilized. For instance,choppers manufactured by Finn and Fram, Inc. of San Fernando, Calif.,U.S.A. may be used.

The aqueous portion of the alkaline aqueous size composition is removedvia drying and the nanoparticles of the inorganic material are caused toadhere to the surface of the fibrous material to provide finelyroughened surfaces as the result of the presence of the nanoparticles ofan inorganic material. Such removal of the aqueous portion of the sizecomposition conveniently can be accomplished by the volatilization ofwater in a heated oven. Representative oven temperatures commonly areapproximately 50 to 300° C., and preferably are approximately 100 to250° C. Infrared, microwave power, or other methods can also be utilizedto dry the fibers. In such cases, the temperature may be below or abovethe above mentioned ranges.

Alternatively in a further embodiment, continuous filaments may becollected using a winder and subjected to the drying and optionalchopping processes at later time, even immediately before incorporationin the thermoplastic matrix material. When collecting rovings ofcontinuous filaments the order of the drying and the optional choppingsteps may be reversed.

The fibrous material having a finely roughened surface as a result ofthe presence of the nanoparticles of an inorganic material is nextincorporated within a thermoplastic matrix material. Such thermoplasticmatrix material commonly is polymeric in nature and becomes molten or isotherwise rendered melt processable when exposed to heat and returns toits original condition when cooled to room temperature. Representativethermoplastic polymeric matrix materials include melt processiblepolyolefins, polyesters, polyamides, polycarbonates, polyethers, liquidcrystal polymers, polyethersulfones, polyphenylene oxide, polyphenylenesulfide, polybenzimidazoles, thermoplastic polyurethanes, etc.Representative polyolefins include polypropylene and polyethylene.Representative polyesters include polyethylene terephthalate andpolybutylene terephthalate. Representative polyamides include nylon 6and nylon 6,6. Polymers and copolymers, such as polystyrene, polymers ofstyrene-maleic anhydride or styrene-maleic acid, polymers ofacrylonitrile-butadiene-styrene, polymers of styrene acrylonitrile,polyetheretherketones, thermoplastic polyurethanes, and polymers ofacrylonitrile, when melt processible may be utilized. Blends ofthermoplastic melt processible thermoplastics also can serve as thematrix material. The thermoplastic matrix material optionally may beasphalt.

A preferred thermoplastic matrix material is polypropylene homopolymeror copolymer with Melt Flow Indices (MFI) between 1 and 100, but higheror lower MFI may be used according to the particular preferences orrequirements. Exemplary polypropylenes include Fortilene HB1801 from BP,Profax 6523 from Basell, or LGF8000 from Dow Chemical. The addition of acoupling agent such as polypropylene grafted with maleic anhydride (suchas Polybond 3200 from Crompton or Exxelor PP1020 from Exxon Mobil) mayalso be included. Other processing additives may also be included in thematrix.

The incorporation of the fibrous material having a finely roughenedsurface as the result of the presence of nanoparticles commonly may beaccomplished by blending while using conventional extrusion equipment,such as twin or single-screw extruder with co- or counter-rotatingscrews. As a result of such blending, a material suitable for injectionor compression molding is formed.

A fiber-reinforced thermoplastic composite articles may be formed by anyone of the variety of molding techniques wherein the fibrous materialhaving a finely roughened surface is incorporated within the continuousphase of a thermoplastic matrix. During such molding step, moldingtemperatures are selected which correspond to a temperature at which thethermoplastic matrix is melt processable.

Representative thermal techniques to form thermoplastic fiber-reinforcedcomposite articles which include as fibrous reinforcement thesurface-roughened fibrous material in accordance with the concept of thepresent invention include compression molding, injection molding, andlong-fiber molding technology. In accordance with the long-fibertechnology the compounding is conducted in-line with injection orcompression molding. For instance, granular long-fiber technology(G-LFT) can be utilized in which surface-roughened filaments areincorporated in the thermoplastic matrix material, are cooled, and thenare pulled into a chopper where they are cut into molding pellets.Alternatively, direct long-fiber technology (D-LFT) can be utilized inwhich in-line compounding of the surface-roughened filaments aredirectly integrated into the molding or part-extrusion process. Thisachieves cost, time and processing savings by integrating thecompounding step into the final molding operation. An intermediatesolidification and remelting of the thermoplastic matrix material isthereby eliminated. It will be recognized by those skilled in the artthat the use of long-fiber technology has the ability to introduceanisotropic material properties within the resulting fiber-reinforcedcomposite articles which are particularly useful in specializedapplications. Also, in accordance with the long-fiber technology fibrousreinforcement of a greater length commonly is made possible in the finalfiber-reinforced composite article which further enhances the mechanicalproperties thereof.

When polypropylene of the Profax 6523 type (Melt Flow Index of 4) isutilized as the thermoplastic polymeric matrix material, moldingtemperatures of approximately 180° C. to 250° C. commonly are employed.Quality glass fiber-reinforced composite articles can be formed in avariety of configurations while using conventional or specializedinjection or compression molding equipment. Representative moldedarticles include automotive or appliance parts or housings, etc.

The enhancement of mechanical properties displayed by the moldedarticles formed in accordance with the present invention makes possibleimproved service qualities during use. For instance, properties such astensile strength, notched and unnotched Izod impact strength, notchedand unnotched Charpy impact strength, modulus, and flexural strength maybe improved over similarly prepared fiber-reinforced composite articleswherein the discontinuous glass fiber reinforcement following injectionor compression molding lacks roughened surfaces as the result of thepresence of nanoparticles of an inorganic material which are provided asdescribed herein. Additionally, it is found that the fiber-reinforcedcomposite articles of the present invention commonly possess improvedinitial color as well as improved color following aging. It is a furthereconomic advantage of the present invention that one has the option ofutilizing a lesser overall quantity of the alkaline aqueous sizecomposition when compared to size compositions of the prior art. Themechanism whereby the presence of the nanoparticles of an inorganicmaterial on the discontinuous glass fibers serves to make possible suchcombination of benefits is considered to be complex and incapable ofsimple explanation. It is believed, however, that such benefits areachieved in part by improved mechanical interlocking of thediscontinuous glass fibers to the thermoplastic matrix material. Also,the surface healing of minor imperfections which inherently are presentin the surfaces of the fibrous material by the nanoparticles of aninorganic material may be achieved. The mechanism whereby improved color(i.e. lower color) additionally is achieved in the resultingdiscontinuous fiber-reinforced composite articles is totally unknown.

The following Examples are presented to provide specific representativeembodiments of the present invention. It should be understood however,that the invention is not limited to the specific details set forth inthe Examples.

EXAMPLE I

An aqueous dispersion of colloidal silica available from Eka Chemicals,Inc. under the Bindzil® 830 designation was selected as the source ofthe nanoparticles of an inorganic material. Such nanoparticles wereamorphous and generally spherical in configuration, possessed a specificsurface area of approximately 300 m²/g, and an average particle size ofapproximately 10 nm.

To 827 g of water were added under agitation 110 g of Michem® ME91735polypropylene grafted with maleic anhydride emulsion serving as afilm-former available from Michelman, Inc., 18 g of A-1100γ-aminopropyltriethoxysilane reactive silane coupling agent commerciallyavailable from Momentive Performance Materials, Witton, Conn., U.S.A.,1.6 grams of Mapeg® 200 ML PEG (200) ester monolaurate surfactant orlubricant commercially available from the BASF Corporation, 43 grams ofthe alkaline aqueous dispersion of silica nanoparticles, and 0.1 gram ofDEE FO PI-35 polysiloxane-based defoamer in neat form and commerciallyavailable from Ultra Additives of Bloomfield, N.J., U.S.A. The resultingaqueous size composition possessed an alkaline pH of 10.5. The silicananoparticles present in the alkaline aqueous size composition had aconcentration of approximately 20 percent, the polymeric film-former wasprovided in a concentration of approximately 60 percent, the reactivesilane coupling agent was provided in an effective concentration ofapproximately 18 percent achieved after in-situ hydrolysis, and thesurfactant and defoamer were provided in a total concentration ofapproximately 2 percent; all based on weight of total solids in thecomposition.

A kiss-roll applicator with a circumference of 45 cm operating at aspeed of approximately 40 revolutions per minute was used to apply as anintimate coating the alkaline aqueous size composition containing thedispersion of silica nanoparticles to a roving of E-glass. The rovingconsisted of approximately 4,000 continuous glass filaments each havingan average single filament diameter of approximately 13.5 μm.

The continuous glass fibers roving bearing such nanoparticles on thefilament surfaces was passed at a rate of approximately 20 meters persecond to a chopper operating at a rate of approximately 130 cuts persecond to form modified discontinuous glass fibers while retaining thepresence of the nanoparticles on the glass fiber surfaces. The resultingdiscontinuous fibers were cut to average lengths of approximately 5 mm.

The resulting chopped glass fibers bearing a coating of the aqueousalkaline size composition were passed through an oven set at 190° C.where the aqueous portion of the composition was removed throughvolatilization resulting in the further adherence of the silicananoparticles to the surfaces of the glass filaments to yield finelyroughened filament surfaces as the result of the presence of thenanoparticles. Following such drying, the silica nanoparticles werepresent in the sized fiberglass in a concentration of approximately 20percent by weight based on the weight of the total sizing solids.

The discontinuous glass fibers having finely roughened surfaces as theresult of the presence of the nanoparticles following drying wereincorporated through blending in a polypropylene thermoplastic matrixmaterial by extrusion using a twin-screw extruder. The polypropylenematrix material was of a polypropylene homopolymer with Melt Flow Indexof 4, and was commercially available from Basell of Frankfurt, Germany,under the Profax 6523 designation.

Pellets of the matrix material suitable for melt processing havingdimensions of approximately 2 mm to 5 mm were formed from the resultingblend by the use of a standard pelletizer. Such pellets then wereinjection molded using a molding machine at a temperature ofapproximately 200° C. to form discontinuous fiber-reinforced compositearticles. Any extruder, pelletizer, or molding machines suitable forprocessing of reinforced thermoplastic materials can be used for suchprocess.

The resulting injection molded articles were subjected to physicaltesting and their properties were compared to similarly preparedfiber-reinforced composite articles in which nanoparticle roughening wasabsent on the discontinuous fiber surfaces. A comparison of the physicalproperties is set forth in Table 1 which follows. The loss on ignition(LOI) is with respect to the surface-roughened discontinuous fibersprior to incorporation in the thermoplastic matrix.

TABLE 1 Property With Nanoparticles Without Nanoparticles Fiber Diameter13.6 μm 13.5 μm Loss on Ignition (LOI) 0.57% 0.66% TensileStrength-Initial 76 MPa 72 MPa (ASTM D638) Tensile Strength With 57 MPa57 MPa Aging (10 days in 95° C. water) Flexural Modulus 3.8 GPa 3.8 GPa(ASTM D790) Yield 198 MPa 182 MPa Flexural Strength 122 MPa 112 MPa(ASTM D790) Initial Color (b value) 7.1 10.4 (Using Colorimeter) Color(b value) With Aging 8.7 13.3 (24 h at 150° C.) Unnotched Charpy Impact53 kJ/m² 45 kJ/m² (ASTM D6110) Notched Charpy Impact 10.5 kJ/m² 8.5kJ/m² Unnotched Izod Impact 637 J/m 613 J/m (ASTM D256) Notched IzodImpact 196 J/m 184 J/m

As indicated, a number of physical properties in the resulting injectionmolded discontinuous fiber-reinforced composition articles includingcolor were enhanced when practicing the present invention. Both theproduct of the present invention and that obtained using the controlsize yielded good strand integrity.

EXAMPLE II

An aqueous dispersion of colloidal silica available from Grace Davisonof Columbia, Md., U.S.A., under the Ludox® SM designation was selectedas the source of nanoparticles of inorganic material. Such nanoparticlespossessed a specific surface area 350 m²/g, and the aqueous dispersionof colloidal silica was included in the alkaline aqueous sizecomposition in a concentration of 15.0 percent by weight.

The additional components of alkaline aqueous size composition were 64.9percent of Hydrosize® PP2-01 functionalized polypropylene aqueousdispersion available from Hydrosize Technologies, Inc. of Raleigh, N.C.,U.S.A., serving as a film former, 17.5 percent of A-1100γ-aminopropyltriethoxysilane reactive silane coupling agent availablefrom Momentive Performance Materials, 2.5 percent Mapeg® 200 ML PEG(200) ester monolaurate surfactant or lubricant available from BASFCorporation, and 0.1 percent of DEE FO PI-35 polysiloxane-based defoameravailable from Ultra Additives. The alkaline aqueous size compositionpossessed a solids content of 6.5 percent and an alkaline pH of 10.3.The resulting alkaline aqueous size composition containing a dispersionof colloidal silica was applied through the use of a kiss-rollapplicator to a multifilamentary roving of 4,000 E-glass filaments eachhaving a diameter of approximately 16 μm, and was dried to produce aroughened surface on the continuous glass filaments as a result of thepresence of the silica nanoparticles. The loss on ignition (LOI) of theresulting surface-roughened glass roving was 0.6 percent.

The glass filamentary roving bearing the nanoparticle-roughened surfacewas passed together with molten polypropylene through a Leistritz ZSE 40GL twin-screw extruder that was equipped with screws designed tominimize damage to the surface-roughened glass fibers. As themultifilamentary glass roving passed through the extruder it was welladmixed with the molten polypropylene intended to serve as thecontinuous matrix phase of a fiber-reinforced composite article.

The resulting thermoplastic polymer-impregnated roving next was passedin the absence of the appreciable cooling to a cutter to form partiallysolidified large pellets suitable for molding. The fibrous reinforcementwas primarily unidirectionally aligned within the resulting pellets.

The resulting large pellets containing the surface-roughened glassfibers in the absence of any substantial cooling were next placed in amold and were compression molded in a Dieffenbacher molding machinehaving a capacity of 5000 kN to form a fiber-reinforced compositearticle in sheet form containing primarily unidirectionally alignedglass fibers as reinforcement within a continuous matrix ofpolypropylene.

The above procedure was repeated with the exception that the alkalineaqueous size composition that was coated on the glass roving lacked thesilica nanoparticles and the Mapeg®200 ML PEG (200) surfactant andlubricant which had been included as a processing aid. In the aqueousdispersion the reactive silane coupling agent was provided in the same17.5 percent concentration, the concentration of the aqueous dispersionof functionalized polypropylene film-former was increased to 82.4percent, and the polysiloxane-based defoamer was present in the same 0.1percent concentration. The alkaline aqueous size composition possessed asolids content of 6.3 percent, and an alkaline pH of 10.1. The loss onignition (LOI) of the resulting glass roving was 0.5 percent.

Representative test specimens were water-jet cut from the compressionmolded sheets, and the physical properties of such compression moldedfiber-reinforced composite articles were evaluated while using the testprocedures of the International Organization for Standardization (ISO).The results of such evaluation are reported hereafter. A comparison ofthe physical properties is set forth in Table 2 which follows.

TABLE 2 Property With Nanoparticles Without Nanoparticles Fiber Diameter16 μm 16 μm Loss on Ignition (LOI) 0.6% 0.5% Tensile Strength 40 MPa 41MPa (Transverse) Tensile Strength 96 MPa 99 MPa (Longitudinal) UnnotchedIzod Impact 279 J/m 286 J/m (Transverse) Unnotched Izod Impact 477 J/m461 J/m (Longitudinal) Notched Izod Impact 105 J/m 94 J/m (Transverse)Notched Izod Impact 288 J/m 158 J/m (Longitudinal) Multi-Axial impact 26J 26 J

It will be recognized that disparities between the transverse andlongitudinal test results are attributable to the general alignment ofthe fibrous reinforcement within the resulting fiber-reinforced testspecimens. As indicated, physical properties such as the Notched IzodImpact are shown to be significantly enhanced when practicing theconcept of the present invention through the use of inorganicnanoparticle roughening on the surface of the fibrous reinforcementpresent within the thermoplastic matrix.

EXAMPLE III

An aqueous dispersion of colloidal silica available from Eka Chemicals,Inc. under the designation of Bindzil® 215 designation was selected asthe source of nanoparticles of inorganic material. Such nanoparticlespossessed a specific surface area 600 m²/g, and the aqueous dispersionof colloidal silica was included in the alkaline aqueous sizecomposition in a concentration of 15.0 percent.

The additional components of alkaline aqueous size composition were 64.9percent of Michem® ME 91735 polypropylene grafted with maleic anhydrideemulsion available from Michelman, Inc., serving as a film former, 17.5percent of A-1100 γ-aminopropyltriethoxysilane reactive silane couplingagent available from Momentive Performance Materials, 2.5 percent Mapeg®200 ML PEG (200) ester monolaurate surfactant or lubricant availablefrom BASF Corporation, and 0.1 percent of DEE FO PI-35polysiloxane-based defoamer available from Ultra Additives. The alkalineaqueous size composition possessed a solids content of 6.3 percent andpH of 10.9. The resulting alkaline aqueous size composition containing adispersion of colloidal silica was applied through the use of akiss-roll applicator to a multifilamentary roving of 4,000 E-glassfilaments each having a diameter of approximately 16 μm, and was driedto produce a roughened surface on the continuous glass filaments as aresult of the presence of the silica nanoparticles. The loss on ignition(LOI) of the resulting surface-roughened glass roving was 0.5 percent.

The glass filamentary roving bearing the nanoparticle-roughened surfacewas passed together with molten polypropylene through a Leistritz ZSE 40GL twin-screw extruder that was equipped with screws designed tominimize damage to the surface-roughened glass fibers. As themultifilamentary glass roving passed through the extruder it was welladmixed with the molten polypropylene intended to serve as thecontinuous matrix phase of a fiber-reinforced composite article.

The resulting thermoplastic polymer-impregnated roving next was passedin the absence of the appreciable cooling to a cutter to form partiallysolidified large pellets suitable for molding. The fibrous reinforcementwas primarily unidirectionally aligned within the resulting pellets.

The resulting large pellets containing the surface-roughened glassfibers in the absence of any substantial cooling were next placed in amold and were compression molded in a Dieffenbacher molding machinehaving a capacity of 5000 kN to form a fiber-reinforced compositearticle in sheet form containing primarily unidirectionally alignedglass fibers as reinforcement within a continuous matrix ofpolypropylene.

The above procedure was repeated with the exception that the alkalineaqueous size composition that was coated on the glass roving lacked thesilica nanoparticles and the Mapeg® 200 ML PEG (200) surfactant andlubricant which had been included to well disperse the silicananoparticles as a processing aid. In the aqueous dispersion thereactive silane coupling agent was provided in the same 17.5 percentconcentration, the concentration of the emulsion of polypropylenegrafted with maleic anhydride film-former was increased to 82.4 percent,and the polysiloxane-based defoamer was present in the same 0.1 percentconcentration. The alkaline aqueous size composition possessed a solidscontent of 6.4 percent, and an alkaline pH of 10.9. The loss on ignition(LOI) of the resulting glass roving was the same 0.5 percent.

Representative test specimens were water-jet cut from the compressionmolded sheets, and the physical properties of such compression moldedfiber-reinforced composite articles were evaluated while using the testprocedures of the International Organization for Standardization (ISO).The results of such evaluation are reported hereafter. A comparison ofthe physical properties is set forth in Table 3 which follows.

TABLE 3 Property With Nanoparticles Without Nanoparticles Fiber Diameter16 μm 16 μm Loss on Ignition (LOI) 0.5% 0.5% Tensile Strength 39 MPa 39MPa (Transverse) Tensile Strength 88 MPa 98 MPa (Longitudinal) UnnotchedIzod Impact 295 J/m 334 J/m (Transverse) Unnotched Izod Impact 472 J/m431 J/m (Longitudinal) Notched Izod Impact 141 J/m 101 J/m (Transverse)Notched Izod Impact 235 J/m 212 J/m (Longitudinal) Multi-Axial Impact 26J 23 J

It will be recognized that similar disparities between the transverseand longitudinal test results are attributable to the general alignmentof the fibrous reinforcement within the resulting fiber-reinforced testspecimens. As indicated, physical properties such as the Notched IzodImpact are again shown to be significantly enhanced when practicing theconcept of the present invention through the use of inorganicnanoparticle roughening on the surface of the fibrous reinforcementpresent within the thermoplastic matrix.

The principles, preferred embodiments, and modes of operation of thepresent invention have been described in the foregoing specification.The invention which is protected herein, however, is not to be construedas being limited to the particular forms disclosed, since these are tobe regarded as being illustrative rather than restrictive. Variationsand changes may be made by those skilled in the art without departingfrom the spirit of the invention.

1. A process for forming modified fibers having roughened surfacessuitable for incorporation in a thermoplastic matrix to form afiber-reinforced composite article comprising: (a) applying as a coatingto the surface of the fibrous material an alkaline aqueous sizecomposition comprising a dispersion of nanoparticles of an inorganicmaterial, and (b) drying said coating present on said fibrous materialto provide a roughened surface on said fibrous material as the result ofthe presence of said nanoparticles of said inorganic material.
 2. Theprocess of claim 1, wherein said fibrous material comprises glassfibers.
 3. The process of claim 1, wherein said fibrous materialcomprises mineral fibers.
 4. The process of claim 1, wherein saidfibrous material is in the form of a multifilamentary roving.
 5. Theprocess of claim 1, wherein said alkaline aqueous dispersion ofnanoparticles of an inorganic material possesses a pH of approximately7.5 to
 13. 6. The process of claim 1, wherein said nanoparticles of aninorganic material possess an average particle size of approximately 3to 40 nm.
 7. The process of claim 1, wherein said nanoparticles of aninorganic material possess an average particle size of approximately 3to 10 nm.
 8. The process of claim 1, wherein said nanoparticles of aninorganic material are silica.
 9. A surface-modified fibrous materialsuitable for incorporation in a thermoplastic matrix to form afiber-reinforced composite article having surface roughening created bythe presence of adhering nanoparticles of an inorganic material formedby the process of claim
 1. 10. A process for forming discontinuousmodified glass fibers suitable for incorporation in a thermoplasticmatrix and the formation of a fiber-reinforced composite article byinjection or compression molding which displays an enhanced mechanicalproperty comprising: (a) adhering nanoparticles of an inorganic materialthat are dispersed in an alkaline aqueous size composition to thesurfaces of glass fibers which are present in continuous form to providefinely roughened surfaces on said continuous glass fibers as the resultof the presence of said nanoparticles of said inorganic material, and(b) cutting said continuous glass fibers into discontinuous lengthswhile retaining said roughened surfaces on said glass fibers as theresult of the presence of said nanoparticles of said inorganic material.11. The process for forming discontinuous glass fibers suitable forincorporation in a thermoplastic matrix according to claim 10, whereinsaid continuous glass fibers of step (a) are selected from the groupconsisting of E-glass, C-glass, A-glass, AR-glass, D-glass, R-glass,S-glass, and mixtures of the foregoing, and possess a diameter ofapproximately 2 to 50 microns.
 12. The process for forming discontinuousglass fibers suitable for incorporation in a thermoplastic matrixaccording to claim 10, wherein said continuous glass fibers of step (a)are E-glass, and possess a diameter of approximately 7 to 30 microns.13. The process for forming discontinuous glass fibers suitable forincorporation in a thermoplastic matrix according to claim 10, whereinsaid alkaline aqueous dispersion possesses a pH of approximately 8 to11.
 14. The process for forming discontinuous glass fibers suitable forincorporation in a thermoplastic matrix according to claim 10, whereinsaid nanoparticles of an inorganic material possess an average particlesize of approximately 3 to 40 nm.
 15. The process for formingdiscontinuous glass fibers suitable for incorporation in a thermoplasticmatrix according to claim 10, wherein said nanoparticles of an inorganicmaterial possess an average particle size of approximately 3 to 10 nm.16. The process for forming discontinuous glass fibers suitable forincorporation in a thermoplastic matrix according to claim 10, whereinsaid nanoparticles of an inorganic material are selected from the groupconsisting of silica, clay, glass, metals, titanium dioxide, zinc oxide,barium oxide, cerium gadolinium oxide, iron ferrite, aluminumpolyphosphate, nanodiamonds, and mixtures of the foregoing.
 17. Theprocess for forming discontinuous glass fibers according to claim 10,wherein said nanoparticles of an inorganic material are silica.
 18. Theprocess for forming discontinuous glass fibers according to claim 10,wherein said alkaline size composition of step (a) additionally includessilane, surfactant, and polymeric film-former.
 19. The process forforming discontinuous glass fibers according to claim 10, wherein instep (a) the nanoparticles of said inorganic material are caused toadhere to said continuous glass fibers by initially coating saidalkaline aqueous size composition on the surfaces of said glass fibersfollowed by removal of volatile components.
 20. The process for formingdiscontinuous glass fibers according to claim 10, wherein in step (b)said continuous glass fibers are cut into discontinuous lengths ofapproximately 2 to 100 mm.
 21. The process for forming discontinuousglass fibers according to claim 10, wherein in step (b) said continuousglass fibers are cut into discontinuous lengths of approximately 3 to 50mm.
 22. Surface-modified discontinuous glass fibers suitable forincorporation in a thermoplastic matrix and the formation of afiber-reinforced composite article by injection or compression moldingwhich displays an enhanced mechanical property as the result of surfaceroughening created by the presence of adhering nanoparticles of aninorganic material formed by the process of claim
 10. 23. A process forforming a fiber-reinforced thermoplastic composite article comprising:(a) applying as a coating to the surface of a fibrous material analkaline aqueous size composition comprising a dispersion ofnanoparticles of an inorganic material, (b) drying said coating presenton said fibrous material to provide a roughened surface on said fibrousmaterial as the result of the presence of said nanoparticles of saidinorganic material, and (c) incorporating said fibrous material bearingsaid roughened surface in a thermoplastic matrix as fibrousreinforcement with the application of heat whereby said thermoplasticmatrix is rendered melt processable.
 24. The process according to claim23, wherein said fibrous material is provided in discontinuous lengthsand injection or compression molding is utilized in step (c).
 25. Theprocess according to claim 23, wherein step (c) forms along-fiber-reinforced thermoplastic composite article.
 26. A process forforming a discontinuous glass fiber-reinforced thermoplastic compositearticle comprising: (a) adhering nanoparticles of an inorganic materialthat are dispersed in an alkaline aqueous size composition to thesurfaces of glass fibers which are present in continuous form to providefinely roughened surfaces on said continuous glass fibers as the resultof the presence of said nanoparticles of said inorganic material, (b)cutting said continuous glass fibers into discontinuous lengths whileretaining said roughened surfaces on said glass fibers as the result ofthe presence of said nanoparticles of said inorganic material, (c)extruding the discontinuous glass fibers having said finely roughenedsurfaces together with a thermoplastic wherein the surface-attachednanoparticles of inorganic material serve to promote the secure bondingof the discontinuous glass fibers within said thermoplastic matrix toform a material suitable for molding, and (d) injection or compressionmolding said material incorporating said discontinuous glass fibershaving said finely roughened surfaces to form a fiber-reinforcedcomposite article which displays an enhanced mechanical property. 27.The process for forming a discontinuous glass fiber-reinforcedthermoplastic composite article according to claim 26, wherein saidcontinuous glass fibers of step (a) are selected from the groupconsisting of E-glass, C-glass, A-glass, AR-glass, D-glass, R-glass,S-glass, and mixture of the foregoing, and possess a diameter ofapproximately 2 to 50 microns.
 28. The process for forming adiscontinuous glass fiber-reinforced thermoplastic composite articleaccording to claim 26, wherein said continuous glass fibers of step (a)are E-glass, and possess a diameter of approximately 7 to 30 microns.29. The process for forming a discontinuous glass fiber-reinforcedthermoplastic composite article according to claim 26, wherein saidalkaline aqueous dispersion possesses a pH of approximately 8 to
 11. 30.The process for forming a discontinuous glass fiber-reinforcedthermoplastic composite article according to claim 26, wherein saidnanoparticles of an inorganic material possess an average particle sizeof approximately 3 to 40 nm.
 31. The process for forming a discontinuousglass fiber-reinforced thermoplastic composite article according toclaim 26, wherein said nanoparticles of an inorganic material possess anaverage particle size of approximately 3 to 10 nm.
 32. The process forforming a discontinuous glass fiber-reinforced thermoplastic compositearticle according to claim 26, wherein said nanoparticles of aninorganic material are selected from the group consisting of silica,clay, glass, metals, titanium dioxide, zinc oxide, barium oxide, ceriumgadolinium oxide, iron ferrite, aluminum polyphosphate, nanodiamonds,and mixtures of the foregoing.
 33. The process for forming adiscontinuous glass fiber-reinforced thermoplastic composite articleaccording to claim 26, wherein said nanoparticles of an inorganicmaterial are silica.
 34. The process for forming a discontinuous glassfiber-reinforced thermoplastic composite article according to claim 26,wherein said alkaline size composition of step (a) additionally includessilane, surfactant, and polymeric film-former.
 35. The process forforming a discontinuous glass fiber-reinforced thermoplastic compositearticle according to claim 26, wherein in step (a) the nanoparticles ofsaid inorganic material are caused to adhere to said continuous glassfibers by initially coating said alkaline aqueous size composition onthe surfaces of said glass fibers followed by removal of volatilematerials.
 36. The process for forming a discontinuous glassfiber-reinforced thermoplastic composite article according to claim 26,wherein in step (b) said continuous glass fibers are cut intodiscontinuous lengths of approximately 2 to 100 mm.
 37. The process forforming a discontinuous glass fiber-reinforced thermoplastic compositearticle according to claim 26, wherein in step (b) said continuous glassfibers are cut into discontinuous lengths of approximately 3 to 50 mm.38. The process for forming a discontinuous glass fiber-reinforcedthermoplastic composite article according to claim 26, wherein saidthermoplastic of step (c) is selected from the group consisting ofpolyolefins, polyesters, polyamides, polycarbonates, polyethers, liquidcrystal polymers, polyethersulfones, polyphenylene oxide, polyphenylenesulfide, polybenzimidazoles, thermoplastic polyurethanes, and blends ofthe foregoing.
 39. The process for forming a discontinuous glassfiber-reinforced thermoplastic composite article according to claim 26,wherein said thermoplastic is polypropylene.
 40. A discontinuous glassfiber-reinforced thermoplastic composite article formed by the processof claim 26, which displays an enhanced mechanical property followinginjection or compression molding containing discontinuous glass fiberreinforcement having finely roughened surfaces as the result of thepresence of adhering nanoparticles of an inorganic material.